Geochemistry of Byzantine and Early Islamic glass from ... · Apollonia, Byzantine glass, Early...
Transcript of Geochemistry of Byzantine and Early Islamic glass from ... · Apollonia, Byzantine glass, Early...
623Geoarchaeology. 2018;33:623–640. wileyonlinelibrary.com/journal/gea
Received: 3 January 2017 Revised: 14March 2018 Accepted: 14March 2018
DOI: 10.1002/gea.21684
R E S E A RCH ART I C L E
Geochemistry of Byzantine and Early Islamic glass from Jerash,Jordan: Typology, recycling, and provenance
GryHoffmann Barfod1,2 Ian C. Freestone3 Achim Lichtenberger4
Rubina Raja1 Holger Schwarzer4
1Centre of ExcellenceUrbanNetwork
Evolutions, AarhusUniversitet, Aarhus,
Denmark
2Department ofGeoscience, AarhusUniversity,
Aarhus, Denmark
3Institute of Archaeology, UCL, London, UK
4Institut für KlassischeArchäologie und
ChristlicheArchäologie,MünsterUniversity,
Münster, Germany
Correspondence
RubinaRaja,CentreofExcellenceUrbanNet-
workEvolutions,AarhusUniversitet, Aarhus,
Denmark.
Email: [email protected]
Funding information
Carlsbergfondet;DeutscheForschungsge-
meinschaft,Grant/AwardNumber: LI-978/4-2;
EliteForskAward;DeutscherPalästina-Verein;
DanmarksGrundforskningsfond,Grant/Award
Number: 119
Scientific editingbyDrewColeman
AbstractTwenty-two objects of glass from the Decapolis city of Gerasa, N. Jordan, with characteristic ves-
sel forms ranging fromHellenistic to Early Islamic (2nd century BCE to 8th century CE) were ana-
lyzed for major and trace elements, and 16 samples for Sr-isotopes. The majority were produced
in the vicinity of Apollonia on the Palestine coast in the 6th–7th centuries CE, and strong inter-
element correlations for Fe, Ti, Mn, Mg, Nb reflect local variations in the accessory minerals in
the Apollonia glassmaking sand. The ubiquity of recycling is reflected in elevated concentrations
and high coefficients of variation of colorant-related elements as well as a strong positive correla-
tion between K and P. The high level of K contamination is attributed to the use of pomace (olive
processing residue) as fuel, and a negative correlation with Cl, due to volatilization as the glass
was reheated. This points to an efficient system for the collection of glass for recycling in Jerash
during the latter part of the first millennium CE. Differences in elemental behavior at different
sites in the Levant may reflect the context of the recycling system, for example, glass from secular
contexts may contain less colorants derived frommosaics than glass associated with churches.
K EYWORD S
Apollonia, Byzantine glass, Early Islamic glass, EMP, Gerasa, Jerash, LA-ICP-MS, Levantine, MC-
ICP-MS, olive fuel, provenance, recycling, Sr isotope, trace elements, trade, typology
1 INTRODUCTION
It is now generally accepted that from the late first millennium BCE
until the late first millennium CE, the ancient glass industry was cen-
tralized. Large-scale natron glass production supplying the entire East-
ern Mediterranean region was centered in only a few locations along
the Palestine coast and in Egypt. Each production center produced
unique glasses due to minor differences in recipe and the local raw
materials, but common for the natron glass types is that they were
made by mixing calcium carbonate-bearing sand with natron (soda)
from salt lakes at Wadi el-Natrun or the Nile Delta (e.g., Brill, 1988;
Degryse, 2014; Degryse & Schneider, 2008; Freestone, Gorin-Rosen,
& Hughes, 2000; Freestone, Leslie, Thirlwall, & Gorin-Rosen, 2003;
Nenna, Vichy, & Picon, 1997). These primary glassmaking centers
exported the raw glass to population centers across the ancient world
where secondary glass workshops remelted and shaped the rawmate-
rial into vessels, windows, and jewelry. Whereas the general outline
This is an open access article under the terms of the Creative Commons Attribution License, which permits use, distribution and reproduction in anymedium, provided
the original work is properly cited.
c© 2018 The AuthorsGeoarchaeology Published byWiley Periodicals, Inc.
of this substantial industry is accepted, issues such as variability with
region, chronology, social and economic context, and the role of recy-
cling remain to be elucidated (Rehren & Freestone, 2015). The present
paper provides indicative results for amajor city in the Levant.
The modern town of Jerash, located about 50 km from Jordan'smodern capital Amman, is the site of the ancient city of Gerasa
(Figure 1). The city, which during the Roman period belonged to the
Decapolis (Pliny,Natural History, 36.45), prospered during the first mil-
lennium CE until an earthquake in 749 CE led to its demise and aban-
donment. The site has been investigated for more than 100 years.
In particular, Yale University conducted large-scale excavations here
in the 1920s, published in the monumental work of Kraeling (1938).
Several find groups were studied, but only little comprehensive work
exists on the typology and chemistry ofGerasa glass (Arinat, Shiyyab,&
Abd-Allah, 2014;Meyer, 1988).
The Danish–German Jerash Northwest Quarter Project has been
on-going since 2011 and investigates the settlement history of the
2 BARFOD ET AL.624
F IGURE 1 Regional map of Syria–Palestine with location of thestudy site of Jerash aswell as surrounding contemporary cities of PetraandUmmel-Jimal. Also shownare glass production sites along the Lev-antine coast at Apollonia, Jalame, and Bet Eli'ezer [Color figure can beviewed at wileyonlinelibrary.com]
highest area within the walled city (Lichtenberger & Raja, 2015, 2017)
(Figure 2). The project explores mainly domestic complexes of this
quarter of the city. Most of the excavated structures stem from the
LateRoman toEarly Islamic periods. During the excavations, evidences
were excavated containing the inventory of houses and among the
finds were glass vessels, most of them fragmented. Here, we present
major and trace elements for 22 as well as Sr isotopic compositions
for 16 glass artefacts excavated during the 2013 campaign of this
project, selected to represent the range of glass forms encountered.
The objectives of this study are twofold. The first is to determine the
main glass types that reached Gerasa and how this reflects the sup-
plies into the city and thus regional trade networks. The second objec-
tive is a detailed characterization of the contaminants and postpro-
duction chemical signatures that became incorporated into the glasses
during remelting in secondary glassworkshops. The signatures provide
clues about the local remelting techniques, furnaces, fuel sources, glass
types mixed during melting and/or added colorants which, ultimately,
reflect the inner workings and infra-structure of Gerasa within a local
and regional context.
2 SAMPLE MATERIAL
During the 2013 campaign of the Danish–German Jerash Northwest
Quarter Project, almost 300 glass items,mostly very fragmented, were
excavated from trenches D–H (Figure 2); most stem from the Middle–
Late Roman and Byzantine–Early Islamic periods. The vessels were
predominantly free-blown. Most Hellenistic, Roman, and Byzantine
fragments were found in secondary strata mixed with other materials
and their original contexts therefore lost.
The glass fragments for analysis were chosen to provide a broad
typological span of diagnostic and datable forms to study long term
developments in glass consumption and recycling purposes within
F IGURE 2 Excavated areas in the Northwest Quarter of Jerash. The glass analyzed in this study was recovered from trenches D–H. Two of thetrenches lie in the central area of the Northwest Quarter (D, E), one is on the southern slope (F) and two are on the northern slope (G, H) [Colorfigure can be viewed at wileyonlinelibrary.com]
BARFOD ET AL. 3625
F IGURE 3 Glass samples 1–21 used in the study. Note that two fragments from object 11 (11a and 11b) were analysed [Color figure can beviewed at wileyonlinelibrary.com]
Jerash. Glass descriptions, typologies, and deduced chronologies are
presented in Figure 3 and details listed in Supplemental Table 1. The
chosen glass samples are not quantitatively representative for all peri-
ods of occupation, since the majority of glass fragments from the
Northwest Quarter excavations stems from the Byzantine and Early
Islamic periods (5th–8th centuries CE) but we have included earlier
representative forms in the analytical sample set.
Early period material is rarely encountered among the glass
finds. Only a few sherds can be assigned to the Hellenistic period
(336 BC–30 BC). They belong to cast grooved bowls showing a
2 BARFOD ET AL.626
TABLE 1 Composition of Corning B glass standard by electronmicroprobe in this study compared to recommended composition
SiO2 Na2O CaO Al2O3 K2O MgO P2O5 TiO2 FeO MnO Cl SO2 CuO PbO Total
Corning B
Recommended valuesa 61.55 17.00 8.56 4.36 1.00 1.03 0.82 0.09 0.31 0.25 0.20 0.45 2.66 0.50
Measuredb 62.17 17.37 8.92 4.29 1.08 1.03 0.80 0.12 0.33 0.24 0.17 0.37 2.90 0.48 100.2
2 Standard Deviation 0.39 0.27 0.16 0.18 0.05 0.04 0.06 0.02 0.05 0.04 0.02 0.02 0.17 0.16
Relative difference −1.0% −2.2% −4.2% 1.6% −8.0% 0.0% 2.4% −33% −6.5% 4.0% 15% 18% −9.0% 4.0%
aRecommended values fromBrill (1999), except PbO and SO2 fromVicenzi et al. (2002).bAverage of 20 analyses duringmultiple analytical sessions.
conical or hemispherical shape (cat. nos. 1–2). The Early Roman impe-
rial period is absent, as are typical forms of the 1st and early 2nd cen-
turies CE. The majority of the Roman glass vessels—as far as can be
determined—can be dated to after the middle of the 2nd until the late
4th centuries CE. These are mostly characterized by a dark weather-
ing patina. Some types of bowls representing common dishes include
examples with a crimped strip-handle (cat. no. 3), a high folded base-
ring (cat. no. 4), a horizontal double fold in the glass wall (cat. no. 7)
and a broad out-folded rim (cat. no. 8). Several other forms and types
were also attested and await final publication. Fine tableware occurs
only in one small fragment of a cut-decorated bowl, which is certainly
imported (cat. no. 5).
The production of some vessel types ranged from the mid to Late
Romanperiods (mid 2nd to late 4th centuriesAD) into the Early Byzan-
tineperiod. This applies for instance tobottles and jugswitha thick trail
below the rim (cat. no. 6) or a spiral trail around the neck (cat. no. 9).
It is the same with conical goblets (cat. no. 11), double kohl tubes (cat.
no. 12), cups decorated with a blue spiral trail (cat. no. 13), and mold-
blown flasks or jugs with vertical ribs (cat. no. 10). Specific glass types
of the Early Byzantine period are polycandelon lamps with a stemmed
hollow foot (cat. no. 15) and goblet types like those with a hollow stem
and a foot with tubular edge (cat. no. 16). A white weathering patina is
characteristic for the glass from this period.
As with other genres of material culture in Jerash such as pot-
tery and architecture, sometimes one cannot determine whether a
glass object has its origin in a Byzantine or in an Umayyad workshop
because no differences inmaterial and shape are discernable. Such dif-
ficulties relate to goblets such as those with a solid stem and a solid
foot (cat. no. 17) and those with a solid foot and a solid stem with
one knob (cat. no. 18) as well as to polycandelon lamps with solid
knobbed stems (cat. no. 19). This suggests a continuous production of
local Byzantine glassmakers under the new Islamic rulers.
Without a diagnostic context, it is impossible to verify the date of
three loose glass tesserae (cat. no. 20)whose associatedmosaic forma-
tions are lost. Cast window panes, also represented in the finds from
the Northwest Quarter (cat. no. 21), were used in Jerash throughout
the periods fromMid-Roman times into the Early Islamic period.
3 METHODS
In preparation for electronmicroprobe (EMP) and laser ablation (LA-)-
ICP-MS analyses, carefully selected fresh glass was mounted in epoxy
and polished.
Major element analyses using natural mineral and glass stan-
dards were performed using the Cameca SX-100 electron microprobe
equipped with five wavelength dispersive spectrometers (WDS) at the
Department of Earth and Planetary Sciences, UCDavis. Quantitative
WDS analysis used an acceleration voltage of 15 kV, a beam current of
10 nA and 10 𝜇m raster lengths. Sodium loss was minimized by count-
ing this element first on the LTAP crystal for 10 s. Similar beam condi-
tion and count timeswereused for analysis of thenatural volcanic glass
standard used for calibration of Si, Na, Fe, and Al and we found repro-
ducibility within 2-sigma error of the reported standard values. Corn-
ing glass standard B was analyzed to monitor precision and accuracy
(Brill, 1999). The given results for Corning B reproduced better than
20% for element oxide concentrations in the 0.1–0.5 wt% range (SO2,
TiO2) and better than 9% for element concentrations above 0.5 wt%
(Table 1). Analyses for samples are reported in Table 2 as averages of
three repeats. Detection limits are ≈300 ppm and the analytical preci-
sion ≈1–2% for the major oxides, including Na2O from which we con-
clude that Na loss due to beam damagewasminimal.
Trace element concentrations were determined by LA-ICP-MS
using an Agilent Technologies 7500a quadrupole ICP-MS coupled to
a New Wave UP-213 nm laser ablation instrument at UCDavis Inter-
disciplinary Center for Mass Spectrometry. The laser is equipped with
a SuperCell sample chamber that uses He as carrier gas. Data are
reported as the mean of six analyses at 70% energy, 80 𝜇m spot size,
10 Hz pulse frequency and 60 sec data acquisition time. Data reduc-
tion was done offline in Microsoft Excel using GSE-G1 as calibration
standard by matching the Si counts for samples and standards to the
SiO2 concentrations determined independently from EMP analyses.
Repeated analysis of GSD-1G and Corning glass B was within 3–5% of
known values for most elements (Table 3).
Sr isotopic analyses. Approximately 50mg fresh glasswas dissolved
in concentrated HNO3 and HF (1:10) and Sr purified by loading the
solutions onto columns with Sr-spec resin from EichromTM. Matrix,
Rb, Ba, and Pb removal was achieved rinsing with 3N HNO3 followed
by elution of Sr with 0.5N HNO3. The procedure was repeated to
ensure complete separation of Sr from Rb. All reagents (HCl, HNO3,
HF) were doubly distilled or Optima grade. Isotopic analysis was done
on a Nu Plasma HR MC-ICP-MS (Nu032) coupled to a DSN-100 des-
olvating nebulizer at UCDavis Interdisciplinary Center for Mass Spec-
trometry. Mass fractionation on 87Sr/86Sr ratios were corrected to86Sr/88Sr= 0.1194 and interferences of 87Rb on 87Sr and 86Kr on 86Sr
were monitored by measuring signal on masses 87 (= 87Rb) and 84
(= 84Kr+84Sr), respectively. These signals were less than a fewmV. The
BARFOD ET AL. 3627
TABLE2
Summaryofsam
pleinform
ationandcompositionsofJerashglassesby
electronmicroprobea
Cat.N
o.
Sample
Color
Typological
Dating
Glass
group
SiO
2Na 2O
K2O
CaO
Al 2O
3FeO
MnO
MgO
P2O
5TiO
2Cl
SO2
Total
Hellenistictype
1Bowlrim
Amber,translucent
2–1stBCE
Hellenistic
67.81(9)
18.92(29)
0.55(2)
8.48(13)
2.57(18)
0.25(5)
–0.52(6)
0.10(3)
0.05(3)
0.96(5)
0.30(3)
100.6
2Bowlrim
Purple,translucent
2–1stBCE
Hellenistic
68.29(26)
16.71(50)
0.68(6)
7.75(15)
2.70(18)
0.51(8)
1.93(10)
0.74(7)
0.09(2)
0.09(4)
0.95(3)
0.16(2)
100.6
2R
Bowlrim
Purple,translucent
2–1stBCE
Hellenistic
68.26(100)
16.75(24)
0.68(3)
7.89(14)
2.72(17)
0.50(6)
1.97(7)
0.76(4)
0.09(2)
0.08(4)
0.95(4)
0.14(4)
100.9
Roman
type
5Bowlw
all
Colorless,
tran
sparen
t3–4th
CE
Roman
Sb71.64(87)
18.76(95)
0.33(5)
4.86(13)
1.89(13)
0.28(3)
–0.48(3)
0.03(3)
0.07(2)
1.18(3)
0.22(3)
99.8
3Bowlrim
Ligh
tgreenishblue,
tran
sparen
t2–4th
CE
Roman
Mn
67.71(122)
18.25(15)
0.73(7)
7.97(14)
2.64(28)
0.36(7)
1.57(4)
0.60(3)
0.12(2)
0.06(2)
0.87(8)
0.27(6)
100.7
4Bowlfoot
Yello
wishgreen,
translucent
3–4th
CE
Roman
Sb,
Mn
69.49(95)
18.11(96)
0.59(3)
6.83(19)
2.14(9)
0.41(3)
0.52(14)
0.51(5)
0.12(2)
0.08(2)
0.97(5)
0.17(6)
100.0
4R
Bowlfoot
Yello
wishgreen,
translucent
3–4th
CE
Roman
Sb,
Mn
69.05(43)
18.56(16)
0.61(4)
7.02(6)
2.20(9)
0.42(6)
0.52(5)
0.53(3)
0.12(3)
0.08(3)
1.01(2)
0.18(4)
100.3
Apollo
niatype
19
Lamp
Green
ishblue,
translucent
6–9th
CE
Apollo
nia
71.81(14)
15.2(41)
0.50(2)
8.38(6)
3.27(19)
0.31(2)
–0.48(4)
0.05(2)
0.08(1)
0.87(6)
0.06(2)
101.1
18
Goblet
Green
ishblue,
translucent
5–7th
CE
Apollo
nia
71.40(56)
15.00(4)
0.54(4)
8.97(34)
3.07(10)
0.40(3)
–0.50(3)
0.11(4)
0.07(1)
0.82(4)
0.07(2)
101.0
17
Gobletfoot
Yello
wishgreen,
translucent
5–7th
CE
Apollo
nia
70.83(10)
15.34(31)
0.64(10)
9.06(35)
3.03(6)
0.42(4)
–0.54(3)
0.12(3)
0.06(2)
0.90(10)
0.06(4)
101.0
8Bowlrim
Palegreen,
tran
sparen
t4th
CE
Apollo
nia
72.79(58)
13.21(28)
0.75(3)
8.97(14)
3.01(7)
0.42(5)
–0.56(3)
0.13(3)
0.07(2)
0.83(3)
0.03(2)
100.8
10
Flask
Palegreenishblue,
tran
sparen
t4–5th
CE
Apollo
nia
71.27(74)
15.26(42)
0.77(3)
8.26(59)
2.96(9)
0.45(7)
–0.68(7)
0.09(2)
0.08(2)
0.89(8)
0.09(2)
100.8
20
Tesserae
Paleblue,
translucent
3–9th
CE
Apollo
nia
72.12(20)
14.23(49)
0.81(4)
8.79(9)
2.97(13)
0.42(6)
–0.55(2)
0.13(4)
0.09(2)
0.85(5)
0.05(2)
101.1
15
Lampfoot
Yello
w-green
,translucent
5–6th
CE
Apollo
nia
71.25(89)
14.22(27)
1.00(7)
9.25(13)
3.08(21)
0.48(5)
0.06(1)
0.59(3)
0.12(4)
0.08(2)
0.69(3)
0.08(2)
100.9
13
Cuprim
Colorless,
tran
sparen
t4–7th
CE
Apollo
nia
70.15(18)
15.60(32)
1.01(4)
8.49(32)
3.13(28)
0.48(8)
–0.59(2)
0.15(2)
0.09(3)
0.67(2)
0.14(3)
100.6
9Jugrim
Palegreenishblue,
translucent
4–5th
CE
Apollo
nia
67.90(21)
14.49(33)
1.09(8)
9.94(15)
3.25(5)
0.97(7)
0.04(1)
0.73(5)
0.18(4)
0.09(1)
0.72(5)
0.07(5)
99.5
21
Window
Yello
wishgreen,
translucent
4–8th
CE
Apollo
nia
70.54(26)
14.84(33)
1.12(4)
9.17(21)
3.16(2)
0.45(5)
–0.59(2)
0.20(8)
0.08(3)
0.69(3)
0.08(4)
101.0
(Continues)
2 BARFOD ET AL.628
TABLE2
(Continued
)
Cat.N
o.
Sample
Color
Typological
Dating
Glass
group
SiO
2Na 2O
K2O
CaO
Al 2O
3FeO
MnO
MgO
P2O
5TiO
2Cl
SO2
Total
12
Tubebase
Yello
wishgreen,
translucent
4–7th
CE
Apollo
nia
70.28(91)
14.98(27)
1.21(13)
8.94(44)
3.05(14)
0.52(9)
–0.75(3)
0.18(4)
0.10(2)
0.66(7)
0.08(3)
100.8
Apollo
niaMntype
11a
Gobletfoot
Paleolivegreen,
translucent
4–7th
CE
Apollo
nia
lowMn
69.96(52)
14.6(22)
1.21(5)
9.56(23)
2.99(25)
0.52(12)
0.06(4)
0.84(4)
0.20(6)
0.10(2)
0.76(2)
0.05(2)
100.9
11b
Gobletfoot
Paleolivegreen,
translucent
4–7th
CE
Apollo
nia
lowMn
69.72(28)
14.74(25)
1.21(6)
9.68(32)
3.03(3)
0.53(9)
–0.89(3)
0.19(2)
0.09(2)
0.75(5)
0.04(5)
101.0
16
Gobletfoot
Palegreenishblue,
tran
sparen
t5–7th
CE
Apollo
nia
lowMn
70.20(25)
16.10(73)
0.82(4)
8.53(21)
2.85(7)
0.52(6)
–0.69(2)
0.12(4)
0.10(5)
0.79(6)
0.11(2)
100.9
7Bowlrim
Palegreen
4th
CE
Apollo
nia
highMn
68.42(48)
16.43(56)
0.98(5)
9.01(19)
2.67(7)
0.53(3)
0.93(5)
0.65(6)
0.13(4)
0.08(2)
0.79(3)
0.13(2)
100.8
6Jugrim
Palegreenishblue,
tran
sparen
t3–5th
CE
Apollo
nia
highMn
69.72(66)
15.68(25)
0.53(4)
8.95(49)
2.87(11)
0.46(5)
0.67(17)
0.79(2)
0.10(2)
0.10(3)
0.79(2)
0.17(3)
100.9
14
Plate
foot
Yello
wishgreen,
translucent
5–6th
CE
Apollo
nia
highMn
68.50(10)
15.51(24)
1.33(6)
10.00(8)
3.07(4)
0.49(4)
0.31(7)
0.65(1)
0.15(2)
0.07(2)
0.69(2)
0.07(6)
100.9
aCompositionsareaverages
ofthreean
alyses
per
sample,excep
tthose
marked“R”representingaverages
of1
0an
alyses
obtained
inalateran
alyticalsession.Values
inparen
theses
aretw
ostan
darddeviationsofthe
meancorrespondingto
thetrailin
gdigits.“–”indicates
belowdetection.
TABLE3
Elemen
talabundances(inpartsper
million)forCorningBandUSG
SGSD
-1Gglassstandardsdetermined
byLA
-ICP-M
Sinthisstudycompared
torecommen
ded
values
LiB
Mg
ScTi
VCr
Mn
FeCo
Ni
Cu
Zn
As
Rb
SrZr
Nb
SnSb
Ba
Ce
Pb
Th
U
ConningB
Measureda
10.7
92.1
6207
1.72
587
190
63
1822
2179
326
716
22115
1616
14
11
146
177
0.17
166
3698
663
0.16
4502
0.81
0.22
Recommen
ded
b16
112
5960
N/A
595
190
66
1870
2200
340
735
22500
1695
N/A
9140
170
N/A
190
3500
690
N/A
4610
N/A
N/A
Relative
difference
c31%
18%
−4%
1%
0%
4%
3%
1%
4%
3%
2%
5%
−21%
−4%
−4%
13%
−6%
4%
2%
USG
SGSD
-1G
Measuredd
42.4
51.2
21379
50.5
7874
43.2
43.1
227
105350
41.3
58.4
41.0
54.2
27.6
38.5
68.3
40.7
39.7
27.6
42.9
68.0
39.5
48.3
39.8
39.9
Recommen
ded
e43
50
21700
52
7430
44
42
220
103400
40
58
42
54
27
37
69
42
42
29
43
67
41
50
41
41
Relative
difference
c1%
−2%
1%
3%
−6%
2%
−3%
−3%
−2%
−3%
−1%
2%
0%
−2%
−3%
2%
3%
5%
5%
0%
−1%
5%
3%
3%
3%
aAveragesof1
0an
alyses
duringmultiplean
alyticalsessions.
bRecommen
ded
values
fromAdlin
gton(2017),Brill(1999),Vicen
zi,Eggins,Logan,andWysoczan
ski(2002),an
dWagner,N
owak,Bulska,H
ametner,andGünther
(2012).
cRatioof(recommen
ded
–measured)/recommen
ded
values
times
100.
dAveragesof1
5an
alyses
duringmultiplean
alyticalsessions.
eRecommen
ded
values
fromGeo
Rem
datab
ase(https://georem.mpch-m
ainz.gw
dg.de).
BARFOD ET AL. 3629
F IGURE 4 Oxide ratio variation diagram of TiO2/Al2O3 versusAl2O3/SiO2 for Jerash Apollonia-type samples compared to majorglass groups in the 1st millennium CE. Oxides are in wt% listed inTable 2. Data sources for comparative groups: HIMT (Group 1 of Foy,Picon, Vichy, & Thirion-Merle, 2003), Apollonia (primary glass fromPhelps et al., 2016; in their Table 2), Rom Mn and Rom Sb (Silvestri,2008; Silvestri et al., 2008), Egypt I and II (Gratuze&Barrandon, 1990).Plot lay-out originally from Schibille et al. (2017) and the location ofthe dashed line from Freestone (in press). Groups below dashed linedescribe glass believed to have been made from sands at productionsites along the Levantine coast (Figure 1) [Color figure can be viewedat wileyonlinelibrary.com]
SRM 987 standard was run after every four samples and the 87Sr/86Sr
ratios of the samples normalized to an accepted value of 0.710248 for
SRM987. Normalized 87Sr/86Sr ratios of 0.705041 (± 0.000013) were
obtained for standards USGS standards BCR-2. This value is within
uncertainty of 87Sr/86Sr value for BCR-2 of 0.705020 ± 0.000016
(Weis et al., 2006).
4 RESULTS
All samples classify as low-magnesium, low-potassium (<1.5 wt% each
of MgO and K2O) natron glasses (Lilyquist, Brill, & Wypyski, 1993;
Sayre & Smith, 1961). Figure 4 compares the TiO2/Al2O3 versus
Al2O3/SiO2 ratios, which may be used to distinguish the main natron
glass groups occurring in the Levant around the 1st millennium CE
(Freestone, Degryse, Lankton, Gratuze, & Schneider, 2018; Freestone,
in press; Schibille, Sterrett-Krause, & Freestone, 2017). All of the sam-
ples plot in the area at the base of the diagram, characteristic of Roman
andByzantine period glass and especially glassmadeusing sands of the
Levantine coast. Based on this and other geochemical characteristics,
17of the22glass fragments analyzed in this study classify asByzantine
glasses of the Levantine type (6 of these with Mn above 300 ppm and
therefore presented separately). The remaining samples include three
Roman glasses decolored by addition of antimony and/or manganese
(1 Sb Roman, 1Mn–Sb Roman, 1Mn Roman) and two glasses from the
Hellenistic period.
The manganese contents of raw glass from glass production sites
in the Levant are below 250 ppm (Phelps, Freestone, Gorin-Rosen, &
Gratuze, 2016). This and other studies define a threshold for the natu-
F IGURE 5 Variation diagram ofMn (ppm) and Ti (ppm) for the threegroups of Byzantine glass we observe in Jerash (Table 4); Apollonia-type glass with Mn below background level (= Byzantine Mn bckgr),with low Mn (= Byzantine Mn > 300 ppm) and with high Mn contents(= Byzantine Mn > 2000 ppm) [Color figure can be viewed at wileyon-linelibrary.com]
ral background level of Mn in glass from the Levant around 250 ppm
(Al-Bashaireh, Al-Mustafa, Freestone, & Al-Housan, 2016; Brems &
Degryse, 2014). Scatter plots of Mn versus other transition metals for
the Jerash samples, showa strong correlationbelow250ppm, but sam-
pleswithMn above this value showamarked departure from the trend
(e.g., Figure 5). This is important for distinguishing between the differ-
ent glass groups observed in our study.
The three glasses which are typologically Roman are natron-based
with CaO and Al2O3 contents below 8 wt% and 2.8 wt%, respectively,
and Na2O concentrations above 17 wt% (Table 2), consistent with
Roman glass produced in the first centuries CE (Jackson, 2005).
Three distinct types of Roman glass are recognized primarily on the
basis of their contents of the decolorizersMn and Sb (Table 4).
1. A colorless bowl (cat. no. 5) classifies as antimony colorless Roman
glass (“Rom-Sb” of Schibille et al., 2017, “Sb” of Jackson & Payn-
ter, 2016) based on its high Sb concentration (5841 ppm) and Mn
below the background level (126 ppm). The relatively low CaO
and Al2O3 contents are characteristic of Rom-Sb glass (Jackson &
Paynter, 2016).
2. Bowl cat. no. 3 belongs to the “Rom-Mn” (or “high-Mn”) group given
its Mn content (12,209 ppm) and Sb below 250 ppm (163 ppm).
Despite the high Mn content which presumably was added as
a decolorant, there is enough Fe2+ in this glass to color it light
greenish-blue. The antimony content, although low, is well above
the background level in raw glass (∼1 ppm; e.g., Brems & Degryse,
2014) and indicates a component of old antimony de/colored glass.
3. Bowl cat. no. 4 has high contents of both Sb (4158 ppm) and Mn
(3733 ppm) and classifies as “Rom Sb—Mn” Roman glass, which is
considered tohave formedby themixingofMn- andSb-decolorized
type glasses (e.g., Freestone, 2015; Jackson & Paynter, 2016; Sil-
vestri, 2008). The yellowish green color is again the result of a rel-
atively high Fe2+/Fe3+ ratio and is typical of glass with a significant
Mn content (Freestone, 2015; Silvestri, 2008).
2 BARFOD ET AL.630
TABLE4
Minorandtraceelem
entcomposition(inpartsper
million)ofJerashglassesby
LA-ICP-M
S
Cat.N
o.
GlassGroup
LiB
Mg
ScTi
VCr
Mn
FeCo
Ni
Cu
Zn
As
Rb
SrZr
Nb
SnSb
Ba
Ce
Pb
Th
U
Hellenistic
1Hellenistic
3.11
135
3046
2.09
300
7.35
10.5
146
2343
1.06
2.83
3.25
6.39
1.31
8.56
524
41.8
1.27
0.54
0.97
221
12.5
7.13
0.88
1.58
2Hellenistic
4.31
190
4310
2.98
509
27.1
17.7
14881
3597
12.2
23.7
29.7
31.7
1.76
7.76
637
51.5
1.54
1.61
1049
322
11.2
80.3
0.92
0.88
Roman
5Roman
Sb3.43
212
2525
2.97
366
7.01
9.05
126
2352
1.09
2.66
4.20
14.1
10.0
4.71
331
45.3
1.40
0.36
5841
133
8.78
10.4
0.75
0.99
3Roman
Mn
3.09
99.3
3425
2.56
373
37.3
17.6
12209
3034
12.9
22.3
14.7
22.9
2.95
8.73
598
44.5
1.35
1.14
163
313
11.8
16.1
0.72
0.77
4Roman
Sb–Mn
3.63
157
2969
2.81
440
14.4
10.7
3733
2876
3.00
5.44
21.4
21.9
12.7
5.57
378
43.8
1.31
11.26
4158
209
9.12
100
0.83
0.97
LevantineI:Apollo
nia-typ
e
19
Apollo
nia
4.01
33.7
2759
2.11
383
8.09
11.9
136
2910
1.13
3.59
2.99
7.05
0.86
7.79
427
40.3
1.57
0.35
0.12
244
12.8
3.39
0.73
0.58
18
Apollo
nia
3.31
39.7
2832
2.53
394
9.25
14.7
124
3430
1.32
4.76
35.8
16.2
1.21
8.43
413
41.0
1.59
2.40
0.19
231
11.7
11.8
0.77
0.67
17
Apollo
nia
3.60
50.2
3150
2.56
411
10.7
15.8
134
3336
1.43
5.07
28.3
14.1
1.22
7.07
428
41.3
1.55
2.26
0.19
235
12.1
13.6
0.79
0.77
8Apollo
nia
3.95
59.0
3429
2.46
473
12.4
18.2
190
4023
2.34
5.19
19.9
11.7
1.59
10.2
444
45.1
1.67
2.50
0.95
241
13.6
37.6
0.87
1.03
10
Apollo
nia
4.15
87.0
4006
2.68
587
13.9
17.9
180
3998
1.96
4.36
5.22
9.22
1.63
10.5
461
62.9
2.00
1.37
0.42
231
14.3
17.7
0.94
0.85
20
Apollo
nia
3.81
67.0
4436
3.09
543
14.0
16.2
153
4275
2.75
5.58
9.93
12.5
2.29
9.19
447
50.1
1.99
0.99
0.93
223
12.5
13.3
0.78
0.73
15
Apollo
nia
3.96
62.9
3378
2.73
495
12.4
21.9
186
3935
5.87
6.45
47.6
14.0
2.03
11.9
428
52.4
1.79
4.26
1.06
230
13.3
52.6
0.86
0.92
13
Apollo
nia
4.06
63.3
3316
2.90
476
12.4
18.3
166
3575
2.09
5.23
20.3
13.2
2.01
12.2
443
54.6
1.82
2.56
1.24
240
12.8
48.2
0.91
1.02
9Apollo
nia
4.20
59.4
3577
2.52
489
11.4
13.8
191
3540
2.37
4.43
14.8
8.74
1.80
10.0
462
53.5
1.86
1.30
0.69
236
13.2
26.8
0.90
0.86
21
Apollo
nia
4.02
70.9
3512
2.62
498
12.1
15.7
166
3689
1.76
5.15
11.2
10.3
1.79
11.6
444
52.8
1.80
1.50
0.71
253
14.3
17.8
0.92
1.04
12
Apollo
nia
4.71
86.1
4430
2.83
604
15.0
18.1
221
4527
6.54
6.48
27.7
12.4
2.17
12.2
415
63.0
2.22
1.51
1.66
238
14.6
73.3
1.04
1.24
Average
3.98
61.7
3529
2.64
487
12.0
16.6
168
3749
2.69
5.12
20.3
11.8
1.69
10.1
438
50.6
1.81
1.91
0.74
237
13.2
28.7
0.87
0.88
StandardDeviation
0.4
1756
30.3
732.0
2.7
3045
91.8
0.9
142.7
0.4
1.8
168.1
0.2
1.0
0.5
8.0
1.0
220.1
0.2
RSD
9%27
%16
%10
%15
%17
%16
%18
%12
%67
%17
%67
%23
%26
%18
%4%
16%
12%
55%
66%
3%7%
75%
10%
22%
LevantineI:Apollo
niaMn
11a
Apollo
nialowMn
4.85
89.4
5345
2.88
558
13.2
16.9
319
4214
3.74
6.06
19.1
12.59
2.64
11.3
474
57.1
2.05
2.79
4.56
238
13.3
50.9
0.98
0.69
11b
Apollo
nialowMn
4.11
76.0
5000
2.94
554
13.8
18.1
319
4384
3.71
6.17
19.0
13.86
2.95
11.1
460
51.4
2.02
2.69
4.97
226
13.0
47.2
0.84
0.61
16
Apollo
nialowMn
4.78
93.1
5276
2.90
565
14.1
18.6
329
4429
3.98
5.95
20.5
12.99
2.98
11.8
487
58.2
2.14
2.77
4.74
244
14.0
54.0
1.05
0.80
7Apollo
niahighMn
4.27
90.2
3926
2.71
497
26.0
16.3
6783
4446
6.40
9.61
65.4
22.28
4.56
10.1
452
49.3
1.79
8.47
453
304
12.5
142
0.91
0.92
6Apollo
niahighMn
3.63
99.5
4543
2.80
527
16.7
17.6
5559
4021
7.98
8.98
15.8
14.62
1.64
7.21
509
58.4
1.92
0.64
0.60
290
13.5
7.30
0.91
0.84
14
Apollo
niahighMn
4.11
60.9
3933
2.84
490
13.3
14.5
2442
3973
3.58
5.90
182
17.08
2.16
14.3
515
49.0
1.78
8.20
40.1
289
13.5
87.2
0.80
0.62
Values
arethemeansofsixseparatespotan
alyses.
BARFOD ET AL. 3631
F IGURE 6 Oxide ratio variation diagram of CaO/Al2O3 versusNa2O/SiO2 for Jerash glass groups, which discriminates between Lev-antine primary productions of glass produced at: (1) Jalame (4th cen-tury; data of Brill, 1988, supplementedwith 3rd century Rom-Mn glassfromSilvestri, 2008, Silvestri et al., 2008), (2) Apollonia (6–7th century,Freestoneet al., 2000, 2008, Tal et al., 2004, supplementedwith vesselsfromPhelps et al., 2016), and (3) Bet Eli'ezer (7–8th century, Freestoneet al., 2000 and unpublished). Original plot lay-out from Phelps et al.(2016). All oxides are in wt% (Table 2) [Color figure can be viewed atwileyonlinelibrary.com]
The major element compositions of the Hellenistic cast bowls (cat.
nos. 1 and 2) are typical for Hellenistic glass (Reade & Privat, 2016)
with Na2O contents of 16.7 and 19 wt%, CaO from 7.8 to 8.5 wt% and
Al2O3 from 2.5 to 2.7 wt% (Table 2) and are also closely similar to the
RomanMn and Roman Sb–Mn types. In Figure 4, they lie between the
Rom Mn and Levantine I types. The purple color of cat. no. 2 is due to
the presence of intentionally highMnO at around 2wt% (e.g., Möncke,
Papageorgiou, Winterstein-Beckmann, & Zacharias, 2014; Schreurs &
Brill, 1984). On the other hand, cat. no. 1 has only background Mn at
146 ppm and is amber which is generally attributed to the presence of
a ferri-sulfide complex (Schreurs&Brill, 1984). Itmaybepertinent that
this glasshas thehighest sulfur contentof thoseanalyzed (0.3wt%) and
the absence of addedmanganese (Tables 2 and 4) is a typical feature of
amber glass (Freestone & Stapleton, 2015; Sayre, 1963), as it is an oxi-
dizing agent and the generation of amber requires reducing conditions.
Glass characteristic of Late Roman–Byzantine Palestine was orig-
inally defined as Levantine by Freestone et al. (2000) and this term
has been heavily used in the literature. It refers to lime and alumina
contents in excess of 8 wt% CaO and 2.8 wt% Al2O3 combined with
relatively low Na2O (<17 wt%) making them distinct from older 1st–
3rd century CE Roman glass (Figure 4; Table 2; Schibille et al., 2017).
Levantine glass has been divided into Levantine I type characterized
by 68–71 wt% SiO2 and 14–16 wt% Na2O and Levantine II type with
relatively higher 73–76 wt% SiO2 and lower 11–13 wt% Na2O con-
tents (Freestone et al., 2000). More recently, it has been recognized
that the original grouping of Levantine I incorporated the products of
at least two different primary productions (Al-Bashaireh et al., 2016;
Phelps et al., 2016; Schibille et al., 2017) and that these canbemore-or-
less separated on the basis of composition: 6th–7th century CE glass
from Apollonia (Freestone, Jackson-Tal, & Tal, 2008; Tal, Jackson-Tal, &
Freestone, 2004) and 4th century CE glass from Jalame (Brill, 1988).
Figure 6 presents our data in terms of CaO/Al2O3 and Na2O/SiO2
ratios, which pull apart glass from the two production sites (Phelps
et al., 2016) and also separate Apollonia glass from natron glass (pre-
viously Levantine II) from the Umayyad production site at Bet Eli'ezer,Hadera (Al-Bashaireh et al., 2016). The reference data for Roman
period Jalame glass are supplemented with data for Rom-Mn glass
from the 3rd century CE Iulia Felix wreck (Silvestri, 2008; Silvestri,
Molin, & Salviulo, 2008) and for the Byzantine Apollonia-type with the
analysis of vessels from Palestine (Phelps et al., 2016).
Whereas the typologically Roman and Hellenistic glasses analyzed
plot on the right-hand side of Figure 6, similar to 4th century Jalame,
the 14 Late Roman–Byzantine (4th century CE or later, Table 2) sam-
ples which have natural levels of Mn or low Mn levels up to 500 ppm
lie to the left, plot in the Apollonia field or have compositions which
straddle the boundary between Jalame and Apollonia glasses. In addi-
tion to their dating, the low manganese contents of these glasses are
consistent with their assignation to Apollonia rather than Jalame since
deliberately added Mn is present in about half of the glass analyzed
from Jalame (Brill, 1988) whereas this has not been observed in pri-
mary glass fromApollonia tank furnaces.
Catalogue numbers 11a, 11b, 16 which have slightly elevated
(≈300 ppm) Mn are separated in the analytical tables and in the
figures, as they are shifted slightly towards the Jalame field (see above;
Figure 6). However, the low Na2O contents of these glasses asso-
ciate them with Apollonia-type production and we consider them as
Apollonia-type glass, with admixing of a small amount of older Mn-
decolorized material. These are henceforth referred to as “low-Mn” as
opposed to glasses with “background” levels of Mn. Cat. nos. 6, 7, and
14 have significantly elevated (> 2000 ppm) manganese and could be
interpreted as Jalame-type glasses (Figure 6; Table 2). However, their
intermediate soda, lime, and alumina contents coupled with elevated
Sb in cat. nos. 7 and 14 (Tables 2 and 4), suggests that these may be
genuinely intermediate, the result of mixing Apollonia-type glass with
older decolorized types, and we group them with the other Byzantine
forms as Apollonia-type glass.
None of the glasses analyzed corresponds to the field of the major-
ity of low-soda high-silica products of the 7th–8th centuryCE furnaces
at Bet Eli'ezer (Figure 6).
5 DISCUSSION
5.1 Origins of primary glass types in Jerash
The strontium isotope data indicate that most of our samples have87Sr/86Sr ratios close to theHolocene seawater (and beach shell) value
of 0.7092 (Table 5, Figure 7). However, the 87Sr/86Sr ratios of Rom-Mn
cat. no. 3 (0.708489) and purple Hellenistic bowl cat. no. 2 (0.708834)
are low. These two samples have the highest Mn contents in our
dataset and also relatively high Sr (Figure 7), characteristics which are
now recognized as likely to reflect the presence of old strontium con-
taminant in the manganese oxide added as decolorant (Gallo et al.,
2015; Ganio et al., 2012). Accepting this, all of the samples analyzed
are consistent withmanufacture from coastal sands.
Figure 8 compares mean values for trace elements expected to
remain undisturbed by later colorant additions for the Jerash glass
2 BARFOD ET AL.632
TABLE 5 Sr isotope compositions of Jerash glass byMC-ICP-MS
Cat. No. Glass Groups 87Sr/86Sr (2𝝈)a
Hellenistic
1 Hellenistic 0.709130 (15)
2 Hellenistic 0.708833 (110)
Roman
5 Roman Sb 0.708903 (15)
3 RomanMn 0.708489 (18)
4 Rom Sb,Mn 0.708987 (14)
Levantine I: Apollonia-type
19 Apollonia 0.709054 (15)
19Rb Apollonia 0.709070 (11)
17 Apollonia 0.708985 (11)
20 Apollonia 0.709132 (14)
13 Apollonia 0.708909 (25)
9 Apollonia 0.709032 (10)
21 Apollonia 0.708989 (16)
Levantine I: Mn
11b Apo lowMn 0.708902 (20)
16 Apo lowMn 0.708907 (16)
7 Apo highMn 0.708904 (18)
6 Apo highMn 0.708993 (13)
14 Apo highMn 0.708987 (14)
Total procedural blank= 0.06 ng Sr
aTwo sigma analytical precision corresponding to the trailing digits.bRepeat analysis.
groups and for primary glasses from Apollonia (data from Phelps et al.,
2016). These fingerprint theLevantine coast as the source for theApol-
lonia glasses from Jerash, and show the strong similarities between
the Rom-Mn, Hellenistic glasses, and primary Apollonia glass. Rom-Mn
glass is generally considered to have originated on the coast of the Lev-
ant (Nenna et al., 1997), and these data are consistent with that view.
TheHellenistic glasses are similar inmajor and trace compositions, and
are likely to have originated in the same region.
In the 1st century CE, the production of antimony-decolorized glass
was established and it appears to have been preferred formore expen-
sive items such as tableware with cut decoration (Jackson & Paynter,
2016). The Roman Sb and Roman Mn–Sb glasses from Jerash differ
significantly from the Byzantine, Rom-Mn, and Hellenistic glasses in
terms of Rb, Ba, and LREE (La, Ce) in particular (Figure 8). This supports
the view that Rom-Sb glass was not a product of Palestine and more
likely originated from Egypt (Degryse, 2014; Schibille et al., 2017).
The results therefore suggest that glass used at Jerash from the
Hellenistic through to the Umayyad period originated mainly from
the tank furnaces of the Levantine coast, with the possible exception
of antimony-decolorized Roman glass of 2nd–4th centuries CE. Glass
types generally considered to have anEgyptian originwhichwere com-
mon inother regions in the4th–7th centuriesCE, such asEgypt I, Egypt
II, HIMT, and Serie 2.1 or HLIMT (Ceglia et al., 2015; Schibille et al.,
2017) are absent from the samples analyzed (Figure 4). However, this
F IGURE 7 Variation plot of 87Sr/86Sr ratios (Table 5) versus stron-tium concentration (in ppm; Table 4) of Jerash Byzantine, Roman, andHellenistic glass groups. Jerash Byzantine group includes glasses withbackground, low and high manganese concentrations. Jerash Romangroup include all three Roman Sb, Roman Mn and Roman Sb–Mnglasses. Original plot lay-out from Freestone et al. (2003). The twoglasses with high Sr and relatively low 87Sr/86Sr are characterized byhigh manganese (Hellenistic glass cat. no. 2 and Roman Mn glass cat.no. 3; Table 4). Apollonia data from Brems et al. (in press) [Color figurecan be viewed at wileyonlinelibrary.com]
F IGURE 8 Trace element concentrations (ppm) related to the sandsource in glass production for the Jerash glass groups normalized tothe weathered continental crust (MUQ of Kamber et al., 2005). Ourgroups are compared to primary glass from Apollonia (Phelps et al.,2016). Jerash Byzantine glasses include low and highMn groups. Notethe logarithmic scale [Color figure can be viewed at wileyonlineli-brary.com]
could be a sampling effect and small quantities of these types might
have reached Jerash; this possibility will be further explored in later
studies.
Of particular interest is that no glasswhichmight have originated in
the tank furnaces at Bet Eli'ezer (Levantine II of Freestone et al., 2000)has been detected. The Bet Eli'ezer furnaces appear to have been in
production fromabout 670CE (Phelps et al., 2016). The absence of this
glass type in Jerash suggests that none of the glasses analyzed date
later than the third quarter of the 7th century CE. This is possible, as
typologically all of the forms could date to late Byzantine times or ear-
lier. Furthermore, Bet Eli'ezer-type glass has been identified at anothersite in Jordan, Umm el-Jimal, located away from the coast but some
BARFOD ET AL. 3633
F IGURE 9 MgversusFe. (b)VversusFe. (c) Ti versusFe. (d)NbversusFe forByzantine Jerashglass groups.All concentrations are inppm (Table4).Reported R2 values are for fitted regression lines for the glass samples with background manganese concentrations. Data for primary glass fromthe furnaces at Apollonia from Phelps et al. (2016) [Color figure can be viewed at wileyonlinelibrary.com]
55 km to the North of Jerash (Al-Bashaireh et al., 2016). However, an
alternative explanation might be that, in the Umayyad period (661–
750 CE), fresh glass from the coast was no longer reaching Gerasa
and that the glass workers were entirely dependent upon recycled
material.
It is pertinent that the glass of the 2nd–4th century CE typically has
a dark weathering patina, whereas the 6th–7th century CE fragments
weather to an opaque white. The precipitation of manganese oxide in
the weathered layers is well-known as the cause of the darkening of
medieval European glass (Schalm et al., 2011) and it seems likely that
this is also the case for Jerash, as the Roman-period pieces typically
have high levels of MnO, whereas the later glasses typically haveMnO
at background levels. The Roman-period antimony-decolorized glass,
cat. no. 5, has low manganese, and also weathers to an opaque white
patina, consistent with these observations.
5.2 Secondary processing phenomena: recycling in
the Apollonia-type glasses
The discussion below will focus on the Apollonia-type glasses since
these are by far the most dominant group in our sample-set and
because they showdistinct features that relate back to production and
postproduction processes in secondaryworkshops. The location of the
glassworkshopswhichmade the vessels in Jerash have yet to be deter-
minedby excavation, but it seems very likely that, like other cities in the
region in Late Antiquity they were in the immediate vicinity.
A number of compositional effects might be anticipated from the
mixing and remelting processes which comprise a glass recycling sys-
tem: (1) mixing of different primary glass compositions, (2) contamina-
tion from the melting furnace/crucibles and iron glass working tools,
(3) contamination with colorants and decolorizers from the incidental
inclusion of old colored glass in the batch, (4) contamination by com-
ponents of fuel and fuel ash, and (5) loss of volatile components to the
furnace atmosphere. By definition, if a glass object is remelted tomake
a new one, then it is recycled, and evidence for remelting is therefore
evidence for recycling.
In terms of mixing different glass types, we have observed above
that the Byzantine glasses with high Mn lie closer to earlier Roman
glasses in terms of major components such as Na2O (Figure 6) and
that this is the result of mixing Apollonia-type glass with Roman Mn-
decolorized glass. No other compelling evidence of mixing of primary
glasses is recognized here, but this process is implicit in some of the
data, for example, the behavior of colorant-related elements, below.
There is a strong correlation between Fe and Mg in the Apollonia-
type glasses from Jerash which is also present for other transition
metal elements such as Ti, V, and Nb (Figure 9). An enrichment in
2 BARFOD ET AL.634
Fe has been observed in Roman Mn–Sb glass from York, UK and
ascribed to contamination from ceramic melting pots or iron blow-
pipes (Jackson & Paynter, 2016). If the Fe was derived from an iron
tool, departure from the trend with MgO would be expected and
this does not occur (Figure 9a). Contamination from the furnace is
a possibility, but the high Mg:Fe ratio of 1:1 indicates control from
heavy minerals such as amphibole, pyroxene, spinel, and zircon (e.g.,
Molina, Scarrow, Montero, & Bea, 2009) rather than clays which
are generally strongly dominated by Fe relative to Mg (e.g., Kamber,
Greig, & Collerson, 2005). Therefore, the covariations in the Apol-
lonia samples are a primary feature controlled by differences in the
accessory mineral assemblage of the individual batches of coastal
sand used for their production. A similar explanation has also been
offered by Schibille et al. (2017) for FeO–MgO covariations in Rom-
Sb glasses that they analyzed from Carthage. However, the Rom-Sb
glasses reported by Schibille et al. (2017) have an MgO:FeO ratio of
2:1, relative to Mg and Fe covariation of 1:1 in the Jerash glasses
(Figure 9). These very different Mg/Fe ratios support the hypothesis
(see above) that the Sb-decolorized glass did not originate in the Lev-
ant, but elsewhere, possibly Egypt.
In addition to iron and other transition metal oxides, an increase in
alumina concentration might be expected if a glass was significantly
contaminated by furnace ceramic during remelting. Figure 6 shows no
enrichment in Al2O3 of the Jerash samples relative to Apollonia pri-
mary glass and we can therefore assume from this and the iron oxide
that contamination of the glass from ceramics (furnace) during any
recycling that occurred was minimal. This differs from the conclusions
of Jackson and Paynter (2016) andmay reflect the arrangement of the
furnace. In the Levantine region, there is limited evidence for the use of
pots or crucibles in which glass was melted and it appears that even at
the secondary stage, the glass was melted in tanks (e.g., Gorin-Rosen,
2000); this was also the case in larger centers in theWest, for example
Roman London (Wardle, 2015). There is evidence, however, for melt-
ing pots at York, UK studied by Jackson and Paynter (op. cit.). Tanks
will typically have had a much larger volume to surface area ratio than
pots or crucibles and the interaction between the walls of the tank
bulk of the glass will have been correspondingly less, explaining the
discrepancy.
A distinctive group of elements, including Cu, Sn, Pb, Co and Sb,
shows different behavior. Figure 10 shows that where crustal values
are available (Kamber et al., 2005), these elements show a substan-
tially higher level of enrichment in our glasses than those elements
associated with accessory minerals. They are the elements associ-
ated with glass coloration and, following earlier studies (Freestone,
Ponting, &Hughes, 2002; Jackson, 1996;Mirti, Lepora, & Saguì, 2000),
it is considered that a significant component originates in the inci-
dental incorporation of small amounts of earlier colored glasses in
recycling processes. This effect of recycling on the distributions of
these elements is conveniently illustrated in terms of the coefficients
of variation (relative standard deviations) for the individual elements
(Figure 11). The colorant elements have very high CVs due to the
imperfect nature of the recycling process and the failure to completely
mix and homogenize separate glass batches. Furthermore, several ele-
ment pairs show very strong correlations, such as Cu–Sn, and Pb–Sb
F IGURE 10 Trace element concentrations (ppm) related to col-orants addition to glasses normalized to weathered continental crust(MUQ of Kamber et al., 2005). Our groups are compared to primaryglass composition from Apollonia (Phelps et al., 2016). Jerash Byzan-tine glasses include lowandhighMngroups.Note the logarithmic scale[Color figure can be viewed at wileyonlinelibrary.com]
F IGURE 11 Coefficients of variation (= relative standard devia-tions) for trace elements in for all Apollonia-type glasses with back-ground levels ofMn (Table 2). Sand-related elements typically have lowCVs whereas those associated with colorants are high. Elements asso-ciated with alkali and ash—U, Rb, and B are intermediate
(R2 of 0.75 and 0.81, respectively), and these appear to reflect specific
coloring agents such as bronze scale and lead antimonate. The implica-
tion is that, whereas the Apollonia-type glasses from Jerash show fea-
tures fully consistent with a single primary production, there has been
significant recycling and this is reflected in the colorants. Furthermore,
analysis of glass from tank furnaces on the Levantine coast indicatesPb
values typically less than10ppm, andCuvalues less than5ppm (Brems
et al., in press; Phelps et al., 2016), whereas with only one exception,
our Apollonia-type glasses contain higher levels (Table 4) suggesting
that the great majority of the Apollonia-type glass analyzed here con-
tains some recycledmaterial.
5.3 Influence from fuel and furnaces during
recycling in Jerash
Evidence that the Apollonia-type glasses had been through one or
more episodes of recycling has been inferred above from the colorant
element concentrations. The effects of workshop practices on glass
composition have been explored experimentally by Paynter (2008)
BARFOD ET AL. 3635
F IGURE 12 Oxide variation diagram of P2O5 versus K2O in wt%(representing contamination from fuel ash) for Jerash Byzantine glassgroups with background and low Mn compared to Byzantine glasscompositions observed at other Levant cities. Data for Petra, Deir AinAbata (Rehren et al., 2010), Ramla, Israel (Tal et al., 2008), and Ummel-Jimal, Jordan (Al-Bashaireh et al., 2016). Primary glass from Apol-lonia from Phelps et al. (2016). R2 value is for fitted regression linethrough Jerashglass group [Color figure canbeviewedatwileyonlineli-brary.com]
who showed that in addition to accumulation of Al and Fe from the
melting pot, remelting of Roman-type soda lime glasses in recon-
structedRomanglass furnaces subjects theglass to contaminationbyK
from fuel ashes and/or vapors. While we can expect the contaminants
to have been strongly controlled by the type of glass, the fuel, the firing
temperatures and the type of clays used tomake the furnace, Paynter'sstudy provide some important clues about potential influences from
furnace and fuel.
Concentrations of K2O and P2O5 in Levantine I glasses from Jerash
are high, up to 1.33 and 0.21%, respectively. Not only are these val-
ues twice as high as in glass from the primary furnaces at Apollonia
(Freestone et al., 2000; Tal et al., 2004), but these two components
are strongly correlated (R2 of 0.88 in Figure 12). The K2O and P2O5
correlation observed for the Jerash glasses is most likely the result
of interaction with the fuel ash and fuel ash vapors during remelt-
ing and/or working as has been observed for Apollonia-type glass at
other contemporary sites such as Petra, Jordan (Rehren, Marii, Schi-
bille, Stanford, & Swan, 2010), Ramla, Israel (Tal, Jackson-Tal, and Free-
stone (2008) and Umm el-Jimal, Jordan (Al-Bashaireh et al., 2016)
(Figure 12). However, other components which might be affected by
fuel ash contamination, particularly MgO and CaO (cf. Al-Bashaireh
et al., 2016) do not appear to have been perturbed in the Jerash glass.
Figure13 shows that relative to observations for theByzantine glass at
Umm el-Jimal, Apollonia-type glass at Jerash shows a lower spread in
CaO (8–10 vs. 7–10.5wt%) and P2O5 (0.05–0.2 vs. 0.05–0.3wt%) con-
centrations as well as lower degree of correlation (R2 of 0.41 vs. 0.56).
This may be due to the configuration of the Jerash furnace(s), so that
the glass was protected from contamination by solid ash, and the con-
tamination was largely from the vapor, but it could also be due to the
type of fuel used.
A plausible fuel for Jerash is olive pits, given the finds of olive crush-
ing mills and olive pits in many layers in Jerash. There is little doubt
F IGURE 13 Oxide variation diagram of wt% CaO versus P2O5 for“High CaO”-group of Byzantine samples observed at Umm el-Jimal(Al-Bashaireh et al., 2016) compared to the Byzantine samples in thisstudy; this group includes samples with background Mn and low Mn.The R2 value is for fitted regression line for this group [Color figure canbe viewed at wileyonlinelibrary.com]
that olives have played a role regionally and oil production in general
was significant (e.g., Ali, 2014). Rowan (2015) has drawn attention to
the extensive evidence for the use of pomace, olive-pressing waste,
as a fuel in antiquity. Olive pits as fuel for glass production are par-
ticularly suitable, since their fire burns hotter than wood and there-
fore they have excellent qualities for glass melting. Large amounts of
charred olive pits were found close to glass furnaces in Beth Shean
(Gorin-Rosen, 2000) and Sepphoris (Fischer&McGray, 1999), but until
now evidence for the actual use of these for firing has not been drawn
from the chemistry of the glass samples. Data on the chemistry of
olive residues is available due to modern interest in their potential as
a biofuel. These indicate 44% K2O relative to 8% CaO for olive pit
ash (Miranda, Esteban, Rojas, Montero, & Ruiz, 2008), 44% K2O rela-
tive to 4% CaO for olive pomace (ECN Phyllis2 database for biomass
and waste; https://www.ecn.nl/phyllis2/) or 28% K2O relative to 18%
CaO for the ash of “olive residue” (Gogebakan & Selçuk, 2009). It is
clear that thepotash to lime ratio of olive pit/residue ash is significantly
higher than those of most hard and soft wood ashes, in which lime
is generally in excess of potash (e.g., Misra, Ragland, & Baker, 1993).
Therefore, furnaces operating with a high proportion of olive pits in
the fuel would produce ash with substantially more K2O than those
firing mainly wood. The high level of enrichment of potash observed
in this study and in other glasses from Jordan strongly suggests that
olive pits were a significant component of the fuel used, consistent
with the archaeological evidence from the region.Miranda et al. (2008)
report that their olive pit ash also contained 3.43% P2O5, which would
volatilize andexplain the correlationobservedbetweenphosphate and
potash.
We observe a negative correlation between potash and chlorine,
which has previously been observed in glasses from Umm el-Jimal (Al-
Bashaireh et al., 2016) andmay also be observed in glass analyzed from
Petra (Rehren et al., 2010) (Figure 14). Chlorine in the primary glass
2 BARFOD ET AL.636
F IGURE 14 Oxide variation diagramofwt%Cl versusK2O (fuel ash)for Levant cities. Data as in Figure 12 [Color figure can be viewed atwileyonlinelibrary.com]
originates from the natron and would normally be expected to show
a positive correlation with soda (Na), also coming from the natron,
and be stabilized in the melt due to sodium–chloride (Dalou, Le Losq,
Mysen, & Cody, 2015). However, given the volatile nature of chlorine,
as well as the alkalis, repeated melting, particularly at high tempera-
ture, inevitably leads toCl (and to a lesser degree alkali) loss (Freestone
& Stapleton, 2015). This does not explain the antithetical relationship
seen for Cl and K in Jerash Byzantine glass (Figure 14). As for Umm el-
Jimal and Petra, we ascribe this correlation to a combination of recy-
cling (leading to chlorine loss) and contamination by fuel ash (leading
to increased potassium). Moreover, the strong negative K–Cl correla-
tion (R2 = 0.63) compared to other sites in the region (Umm el-Jimal at
0.25 and Petra at 0.24), in addition to even stronger positive K–P cor-
relation (R2 = 0.88; Figure 12), suggests that glass recycling was more
intensive at Jerash.
Jackson, Paynter, Nenna, and Degryse (2016) have recently sug-
gested that a negative correlation between CaO and Cl among Roman
glass groups and experimental glass synthesized using Egyptian natron
is a signature of primary glass production. The lack of a similar cor-
relation among the Byzantine glasses of Jerash (R2 = 0.2) does not
exclude this possibility, but does suggest that additional factors affect
Cl and Ca in Levantine glasses. Based on our current understand-
ing of chlorine solubility in silicate melts, chlorine is expected to
increase with the abundance of network-modifiers (e.g., monovalent
and divalent cations (Na+, K+, Ca2+, Mg2+, Mn2+, Fe2+, etc.) in excess
of those needed to locally charge balance Al3+ (Carroll, 2005; Metrich
& Rutherford, 1992; Veksler et al., 2012). This expectation is realized
for medieval and postmedieval glasses where Na and Cl are positively
correlated (Schalm, Janssens, Wouters, & Caluwé, 2007; Wedepohl,
2003) and supported by evidence of immiscible droplets of sodium
chloride in ancientCl-rich glass soda lime–silica glasses (Barber&Free-
stone, 1990; Barber, Freestone, &Moulding, 2009). Finally, the impor-
tance of alkali–Cl complexes in the melt and inevitability of Cl loss
during fusion are corroborated by the relatively high chlorine con-
tents of Roman amber glass which have been suggested to be the
result of relatively short melting durations used to preserve the color
(Freestone & Stapleton, 2015). In conclusion, our observation that
chlorine abundance is antithetical to potash for Jerash Byzantine glass
and the lack of demonstrable correlations with soda and lime is con-
sistent with recycling, and thus not a feature of primary glass produc-
tion. We are not proposing that Cl abundance is a universal tracer of
recycling, melting duration or melting temperature, but rather, when
one considers glasses of similar major element composition from sim-
ilar technological context, chlorine content coupled with correlations
(or not) with other glass constituents is a useful indicator of recycling.
5.4 Compositional dependence upon the context of
the glass recycling economy
The Jerash data emphasize the complexity of the glass recycling pro-
cess and the dependence of the composition of the recycled glass upon
the local social context. It has been observed that the characteristics of
recycling differ from those in some western contexts, such as York, as
contamination from container ceramics is not apparent. Furthermore,
the elevated values and strong correlations for potash and phosphorus
observed here are not as apparent inwesternRoman glasseswhich are
believed to have been recycled (e.g., Freestone, 2015; Silvestri, 2008)
or even in Apollonia-type glass from Israel (Phelps et al., 2016) and this
may be related to the fuel used.
It is also noted that in Umm el-Jimal, in northern Jordan, Apollonia-
type glasses show a greater overall enrichment in trace metals gener-
ally added as colorants, where Cu and Pb enrichments are detectable
using EPMA rather than the trace levels observed here (Al-Bashaireh
et al., 2016). This is likely to stem from the nature of the reservoir
of glass undergoing recycling. The Umm el-Jimal glass was recovered
from churcheswhere storage of colored glasses frommosaics for recy-
clingmight beexpected, as hasbeenobservedatPetra (Marii &Rehren,
2009). We speculate that this led to relatively high contents of glass
colorants in the glass from Umm el-Jimal. The glass from Jerash ana-
lyzed here originates from domestic houses, shows relatively weak
enrichment in colorant elements but strongevidenceof recycling in the
fuel-related components.
There is substantial archaeological evidence from Jerash which
attests to the collection of glass possibly for recycling. Such glass heaps
stem from the churches and especially from the passage north of St.
Theodore and from a room under the north stairs from the Fountain
Court (Baur, 1938 in: Kraeling 514–515). Also, evidence for already
recycled material in the form of glass cakes probably prepared for the
production of glass tesserae has been found in Jerash in the so-called
Glass Court (Baur, 1938 in: Kraeling 517–518). Future work, compar-
ing glass associated with the churches with that from more secular,
domestic contexts, might cast light on the organization of the glass
industry in the Levant at this time.
6 CONCLUSIONS
The excavated glass from Jerash, Jordan, dating to between the Hel-
lenistic and the Late Byzantine periods, derives mainly from the Lev-
antine coast with some, possibly Egyptian, antimony-decolorized glass
BARFOD ET AL. 3637
in the Roman period. The Byzantine glass, which dominates the assem-
blage, derivesmainly from the tank furnaces located in or aroundApol-
lonia. A considerationof themanganese contents of theApollonia-type
glass indicates that it is generally present at background levels, and
where present is the result of remelting andmixing ofRomanglass dur-
ing recycling.
Significant evidence for recycling is observed in the formof elevated
potash and phosphate contamination from the fuel, as well as elevated
transitionmetals. Concomitantly, therewas adepletion in chlorine, due
to volatilization at high temperature. For the first time, we draw atten-
tion to the effect of recycling on the coefficients of variation of trace
elements in the glass. These types of indicator can provide clues as to
the relative intensity of the recycling process,which elemental concen-
trations alone do not.
Despite the apparent proximity of Jerash to primary glass produc-
tion sites near the Levantine coast, an efficient system for recycling of
old glass must have been in place. The implication of a well-organized
recycling system in Jerash suggests limited glass import from the Lev-
antine coast and elsewhere, which is supported by the finds of only few
Romanglasses anda lackofEgyptian-typeglasses. The localizednature
of recycling in Jerashdisplays important regional differences,whichwe
relate to differences in interaction zones and proximity to the produc-
tion sites at theMediterranean coast.
The characteristic K-enrichment observed at Jerash and other Lev-
antine locations has implications for the type of fuel used and is likely
to indicate a significant component of olive-pressing residue. Differ-
ences between Jerash and other sites in the region such as Umm
el-Jimal suggest that the nature and degree of over-printing of pri-
mary compositionsby secondary recyclingprocesses are specific to the
context within which the recycling took place. Technological factors
relating to local practice, as well as the types and quantities of glass
available for recycling, may provide a fingerprint of the secondary
workshop. In favorable circumstances, this may allow the attribution
of glass vessels to secondary workshops through elemental analysis.
The phenomenon of recycling fits well to the overall economic situa-
tion of the cities in the region of the 7th–8th centuries CE. The towns
underwent a considerable process of on the one hand urban indus-
trialization and on the other localization of trade networks (see e.g.,
Avni, 2014, 290–294;Walmsley, 2000, 305–309; 321–329; 335–337).
Both processes are apparent in recycling which attests to local pro-
duction within the city and limited supply of (or high demand for) raw
materials.
ACKNOWLEDGMENTS
We would like to acknowledge the generous funding received for the
undertaking of theDanish–German JerashNorthwestQuarter Project
since 2011 from The Carlsberg Foundation, The Danish National
Research Foundation (grant number 119), Deutsche Forschungsge-
meinschaft, Deutsche Palästina-Verein, EliteForsk Award, and H. P.
Hjerl Hansens Mindefondet for Dansk Palæstinaforskning. Further-
more, we thank Greg Baxter at the UCDavis thin section lab, Sarah
Roeske at theUCDavismicroprobe lab and Justin Glessner at theUCD
Interdisciplinary Center for Mass Spectrometry. We thank Stephen
Koob at the Corning Museum of Glass for providing us with Corning
glass standards. GHB acknowledges support by the Danish National
Research Foundation for the Niels Bohr Professorship at Aarhus Uni-
versity. We thank Charles Lesher, two anonymous reviewers, and the
associate editor for providing constructive comments that significantly
improved this paper.
ORCID
Gry Hoffmann Barfod http://orcid.org/0000-0002-7000-0757
Ian C. Freestone http://orcid.org/0000-0002-8223-4649
Achim Lichtenberger http://orcid.org/0000-0003-2653-9859
Rubina Raja http://orcid.org/0000-0002-1387-874X
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How to cite this article: Barfod GH, Freestone IC, Licht-
enberger A, Raja R, Schwarzer H. Geochemistry of Byzan-
tine and Early Islamic glass from Jerash, Jordan: Typology,
recycling, and provenance. Geoarchaeology. 2018;1–18.
https://doi.org/10.1002/gea.21684 2018;33:623–640. https://doi.org/10.1002/gea.21684